[CRIU] Criu mod to restore files to state when checkpoint taken ...

[Tycho Andersen]

Hi Chris,

On Wed, Jan 07, 2015 at 02:19:32PM -0500, Christopher Covington wrote:
> On 01/03/2015 09:36 AM, Tycho Andersen wrote:
> > On Fri, Jan 02, 2015 at 01:22:15PM -0500, Christopher Covington wrote:
> >> Hi Pavel,
> >>
> >> On 12/31/2014 08:50 AM, Pavel Emelyanov wrote:
> >>> On 12/31/2014 03:53 PM, "Mark O'Neill" wrote:
> >>
> >>>> 3. The required kernel functions (described on Criu website) must be
> >>>> added as modules (-=m) and not hardwired into kernel (=y) in Linux
> >>>> config file.
> >>>
> >>> This is strange. What problems have you seen with all-in kernel?
> >>
> >> At least for me, commit 2b5d06817f1bb2b28eec50b6705b1584435e580b introduced
> >> the following, which is actually spurious:
> >>
> >> (00.098217) Error (util.c:576): exited, status=1
> >> (00.164971) Error (util.c:576): exited, status=1
> >> (00.216945) Error (util.c:576): exited, status=1
> >> (00.296716) Error (util.c:576): exited, status=1
> >> (00.368518) Error (util.c:576): exited, status=1
> >>
> >> I originally proposed [1] a somewhat complex change of probing
> >> /proc/config.gz, but I think a quick and actually more general (as it doesn't
> >> require /proc/config.gz which is itself a configuration option) fix is to pass
> >> an fd to /dev/null into the cr_system() call.
> > 
> > Yes, the /dev/null trick seems a little nicer. Let me know if you want
> > me to send a patch; I haven't had much time for criu recently, but I'm
> > happy to fix the mess I created :)
> 
> Unfortunately, my instance of that change doesn't actually work. Only the
> forked child uses the file descriptors passed as arguments to cr_system() in
> util.c. The error handling logic of the parent uses pr_err, which is a macro
> around print_on_level and uses the log fd.

Just looking into this a bit more, it looks like more recent versions
of modprobe are smart enough to look at the statically built modules
and exit 0 if the module was built statically. My modprobe --version
shows:

$ modprobe --version
kmod version 18

I'm not very familiar with how all this works, maybe it is a fairly
recent change?

Also, I don't have a /proc/config.gz, so even if we parsed that, since
it doesn't exist on all systems we may still get spurious errors.

Tycho

> Chris
> 
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